The use of plasma arc torches to cut workpieces is well-known. It is also known to provide control systems for such plasma arc torches which control the operation of the torches such that the torches establish an arc between the torch and the workpiece at a starting point, move along a predetermined path of travel in accordance with the pattern in which the workpiece is to be cut, and stop such movement at a stopping point and extinguish the arc. In such control systems, the order to extinguish the arc is not issued by the control system program until the torch has reached the stopping point and ceased its movement. During the time delay between issuance of the extinguish order and actual extinguishment of the arc, there usually is a voltage increase which results in waste of electrode material and other undesirable effects.
Plasma arc torches may also be used to mark, but not cut, workpieces by forming a shallow groove in the surface of the workpiece. With previous control systems, plasma arc torches could not be used effectively for precision marking because the torches were not extinguished at the precise end or stopping point of the marking and formed a deeper dimple or hole at the end of the marking.